Egg laying in the marine gastropod Aplysia is a model system for neuroethological analysis of hormonal control of behavior. We propose to extend our behavioral analysis of egg laying with electrophysiological and morphological studies of the motor networks that generate the rhythmic head movements underlying egg deposition. Chronic electromyograms (EMGs) as well as whole-nerve recordings are combined with simultaneous selective cell-body recordings in the intact animal and with intracellular recordings when the intact animal is subsequently reduced. To improve the correlation between neuronal and behavioral patterns, we record from relatively large populations of axons and muscle fibers. To establish a direct link between the neuronal populations in intact and reduced preparations, the experiments are conducted "in tandem" using the same implented electrodes throughout. Digital analysis is used to recognize unitary signals in two-channel recordings on the basis of spike amplitude and temporal offset, and to relate directly the axonal spikes to those recorded from the central cell body and to the potentials recorded peripherally from muscles. The long term goal of this project is to specify the neuronal and hormonal components of the rhythmic central pattern generators (CPGs) underlying natural egg deposition. The immediate goal of this proposal is to identify the motoneuron populations producing the head oscillations by: (1) Recording EMG activity from head and neck muscles to correlate with video monitors of head oscillations during triggered egg deposition in intact animals; (2) Monitoring motoneuron activity with whole nerve electrodes to correlate with EMGs during triggered egg deposition; (3) Backfilling central cell bodies from previously monitored muscles or small nerve branches; (4) Recording selectively from individual identifiable motoneurons in intact animals; (5) Impaling and characterizing target neurons in reduced preparations that correlate with nerve and muscle recording; (6) Determining the behavioral relevance of hormonally-induced increases in respiratory pumping frequency. The proposed studies will extend the usefulness of egg laying in Aplysia as a model system for neuroendocrine coordination in more complex organisms.